I got this from John Shaw of Bella Enery that I thought was interesting and wanted to include it here with this video:

So really the only reason to look at a bldg-tied system is to get better production, more tilt. Price to the integrator is about the same (ballast costs more in racking but less in labor). So why not always do tilted for better production? The issue or difference is in the fact that the warranting roofer has you over a barrel if we pop the membrane; they must be the ones who seal each penetration in order to keep warranty and they will charge from $25-$75 per penetration for flashing. How many flashings? A 100kw system tilted at say 30deg. will need – depending on the wind zone and what we tie into – 300 holes, easily so that is from $7,500-$22,500 extra cost to get you that extra production. In most cases it is not worth the added 8% in kwh per year. You’d get 15,000 more Kwh but on an SG rate that saves you only $750 additional in utility costs per year; $1500 on a C rate form Xcel… As you can see, if you have to pay the roofer $10,000 extra it is gonna take a long time to pay off that choice of having gone for a better tilt, structure tied… Most businesses choose ballasted. Pics attached…

Oh yeah, the other thing is a tilted system can easily stand 10’ at back of array, a ballasted system is less than 1’ high – some people want it seen, others don’t…